Automatic pasty-hue telephone system



W. L. CAMPBELL.

AUTOMATIC PARTY LINE TELEPHONE SYSTEM.

APPLICATION FILED JULY 31. 1906. IILNEWED IuIIE 2i.

l 9 I 9. Patented Jan. 27, 1920.

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AUTOMATIC PARTY LINE TELEPHONE SYSTEM.

APPLICATION HLED JULY 31, 1906.

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AUTOMATIC PARTY LINE TELEPHONE SYSTEM.

APPLICATION FLLED JULY 31.1906. RENEWED. JUNE 21 Pateutd J an. 27, 1920.

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WILSON L. CAMPBELL, 0F CHICAG, ILLINGIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO AUTOMATIC ELECTRIC CGMPN'Z", A CRPORATIGN OF ILLINOIS.

AUTOMATIC PARTY-LINE TELEPHONE SYSTEM.

Application led July 31, 1866, Scra No. 328,545.

To all whom z't may concern:

Be it lfuown that l, lJViLsoN L. CAMPBELL, a citizen of the United States of America, and resident of Chicago, Cook county, Illinois, have invented a certain new and useful Improvement in Automatic Party-Line Telephone Systems, of which the following is a specilication.

My invention relates to automatic telephone systems in general, and more particularly to telephone exchange systems in which selectors and connectors, or other suitable automatic switching machines, are located at the exchange or central station and controlled by calling subscribers for automatically connecting their telephone lines with the lines of the called subscribers, and especially to automatic exchange systems of this character in which subscribers party lines are employed,,necessitating the automatic removal of the guarding potentials when any party line subscriber calls another subscriber on the same line-that is to say, necessitating the automatic removal of the guarding, potential which is ordinarily employed for preventing` seizure of the calling line by other subscribers, thus permitting a party line subscriber' to call back on his own line, so to speak.

Generally stated the object of my invention is the provision of an improved and highly eilicient automatic party line telephone system.

mpecial obyects of my invention aie the provision of improved means for enabling a party line subscriber to automatically call and obtain connection with another subscribers station on the same line; the provision of improved means for automatically removingA the guarding potential established over the private normal of a calling party line, thus preventing the automatic release of the connector when it seizes the calling line-which is also, of course, the called line, inasmuch as it belongs as well to the called subscribci-the said connector having provisions for establishing such a guarding potential as will preclude seizure of the party line while the two subscribers thereon are conversing; and the provision of certain details and novel features of improvement and combinations tending to increase the general efficiency and serviceability of an automatic telephone exchange system of this particular character.

Specification of Letters Patent.

Patented Jan. 27, 1920.

Renewed June 21, 1919. Serial No. 305,919.

To the foregoing and other useful ends, my invention consists in matters hereinafter set forth and claimed.

In the accompanying drawings, Figure 1 is a diagrammatic representation of a party line terminating at the central office in a selector A, which selector is suitably conneet-ed to the battery B, and which party line comprises the substations C, D and E, showing the selector A connected with the connector l?, the subscriber C having called the subscriber D, the system involving` the principles of my invention. v

Fig. 2 is a diagrammatic perspective view of the first-selector.

Fig. 8 is a similar View of the connector.

The substation may be of anyA suitable or approved type. The selector A is of the general type shown in 1Patent No. 815,321, or of any other suitable type.

The connector F may also be of any suitable or approved type, and the one herein shown is an improved connector of the general type described in Patent No. 815,176.

The selector is provided, in addition to the parts well known, with an improved bridgecut-off-relay 2. Said relay has one terminal permanently connected to the battery B, while the other terminal is connected to the side switch private wiper contact 3 and with the winding 4L of the private normal relay 5. The said bridge-cut-off-relay 2 is provided with four springs 6, 7, 8 and 9. rThe springs 8 and 9 control the circuit between the vertical line relay 10 and the battery B, and the springs 6 and 7 control the connection between the switch shaft spring 11 and the rotary line relay 12 and, therefore, between the rotary line conductor 13 and the'rotary line relay 12 whenever the switch shaft springs 11 and 14 are in contact. The bridge-cut-otf-relay is adapted to be energized whenever the selector A calls back on its own line, or when some other subscriber calls the line to which the said` selector is allotted. The private normal relay 5 is provided with two windings t and 15. One of the terminals of the Winding 15 is permanently connected with the battery B and the other terminal is connected with.. the spring 17 of the rotary line relay 12, so that the rel-ay 5 is adapted to be energized whenever the rotary line relay 12' presses the spring 17 onto the ground spring 18. The winding e of the private normal relay has one terminal connected with the bridgeeut-o-relay 2 and the other terminal is connected to the s ring 19 controlled by the relay 5 itself. he said relay 5 also controls two other springs 20 and 21, and the spring 20, it will be noticed, is connected with the private normal conductor 22. Under certain conditions the springs 19 and 20 are brought into contact by the private normal relay 5 while the private normal conductor 22 is grounded, and at such time the private normal relay 5 and the bridge-cut-o-relay 2 lare energized in series. This, however, occurs only when one of the subscribers of the party line calls back on his own line. Normally, the springs 2O and 21 are in cont-act, so that the private normal conductor 22 is maintained 1n connection with the bridgecut-oH-relay 2, and so that when a subscriber calls in upon the line allotted to the selector A, he energizes the bridge-cutoff relay 2 at the selector by grounding the private normal condurtor 22 at the connector. The selector is, of course, in addition provided with the usual vertical magnet 23, rotary magnet 24, release magnet 25, switch-shaft 26, double dog 27, private bank 28, line bank 29, private wlper 30 and line wipers 31 and 32. The vertical ma net 23 controls the vertical movement of t e shaft 26, and the rotary magnet 24 the rotary movement of the said sha The rivate magnet 16 controls the side switch and certain circuits, such as the release circuit and the circuit of the vertical magnet 23.

The substation, as shown at C, is provided with the usual receiver 33, transmitter 34, battery 35, induction-coil 36, switch-hook 37, ringer 38, condenser 39, lock-out relay 40, and calling device of any suitable type but which is here shown comprising the buttons 41 and 42, springs 43 and 44, contact points 45 and 46 and round post 47. There are also provided, o course, the release springs 48, 49 and 50 `and other details essential to an automatic telephone adapted to be used in a system of this kind. It will be understood that all of thc substations are alike, and throughout the drawings like reference characters will refer to like parts.

The connector F herein shown has a vertical line relay 51, a rotary line relay 52, a vertical magnet 53, rotary magnet 54, release-magnet 55, private magnet 56, and ringer relay 57. The switch-shaft 58 is as usual provided with the private wiper 59 and the line wipers 60 and 61, which former is adapted to engage the private bank 62 and the latter wipers the line bank 63. The connector F also has a vertical back-bridge 'relay '147 and a rotary back-bridge relay 148, the function of which will be fully described.

It will be assumed that the substation C is g2-129, D #220 and substation E #320, and that the subscriber at substation C in calling the subscriber #220 at substation D operates the calling device three times, once for the first digit 2, once for the second digit 2 and once for the third digit O. The subscriber removes his receiver from the switch-hook 37 and thereby causes the ground springs 64 and 65 to close connection and thereby place the ground post 47 in connection with the ground terminal G of the battery B by way of the substation ground G1, and at the same time he removes the ringer 38 from across the line when the switch-hook cam arm 66 leaves the spring 67. Furthermore, the secondary circuit comprising the receiver 33 and secondary winding 68 of the inductioncoil is bridged across the line when the springs 69 and 70 are brought into contact. The subscriber then proceeds by pressing the signaling button 41 twice, causing it each time to leave the Contact oint 45 and to engage the ground post 4 The vertical line relay 10 of the first-selector A is thereby energized twice. The energizing circuit may be traced from ground G1 to the ground post 47, thence over the vertical line conductor 71 and conductor 72 to the vertical line relay 10, thence through tbe bridgecut-off relay springs 8 and 9 to the battery lead 73 and through battery B to ground G. The vertical line relay 10, therefore, attracts its armature twice and forces thc spring 74 onto the ground spring 18, thus energizing in turn each time the vertical magnet 23. The circuit through said magnet permits a current to How from ground G2 through the springs 18 and 74, conductor 75. private springs 76 and 77. conductor 78, side switch wiper 79. contact point 8O to the vertical magnet 23, thence to the battery lead 73 and through battery B to ground G. Each time that the vertical magnet 23 is energized the switch-shaft 26 is raised one step. so that by energizing the vertical magnet 23 twice the switch shaft wipers 30, 31 and 32 are raised to the second level to a position opposite the first contact of the second level of their respective banks. The rotary button 42 is then pressed once so that the spring 44 engages the ground post 47 once and as a result energizes the rotary line relay of the selector A. The current passes from ground G1 of the substation to the ground post 47 and thence to the rotary line conductor 13. through the switch shaft springs 14 and 11, bridge-cut-o' relay springs 6 and 7, conductor 80, rotary line relay 12 to the battery lead 73 and through battery B to ground G. The rotarv line relay 12 being operated once forces the spring 17 onto the ground spring 18 once and closes the circuit for energizing the private magnet 16. This circuit may be traced from ground G' through the springs 13 and 17, conductors 81 and S2 to the private magnet 16, thence to the battery lead 73 and through battery 13 to xground (l. lVhen the private magnet 16 operates, the side switch retracting,v spring` 83 draws the side switch into second position, when the escapeinent iingger Si clears the esci peinent teeth 35 and 8G. When the side switch passes to second position the side switcl'i unici? 37 engages the conizact point and an energizing circuit is then established for operating the rotary ma@ not Q4. filhe current Ytlows from ground G3 to the Contact point 33, thence through the side switch wiper 37, conductor 39 and through the rotary magnet 2i and interrupter ii-ings 90 and 01 to the battery lead 7 3, thence through battery B to ground The rotary magnet upon attracting; its armature 9? rotates the shaft Q0 one step and drives the private wiper 30 into engagement with the tiret Contact ci' the second level of the private bank 528. lit the rst trunk line is busy the rotary magnet continues to operate step by step until an idle trunk line is found, and it the first trunk line is busy the first private Contact will be grounded and the private magnet 16 will become ener- ,qized by flow oi current troni the battery B te the grounded private contact, thence through the private wiper 30', side switch wiper 03. contact point 9i, conductors 95 and to the private magnet 1G, thence through. the battery lead 73 and through battery B to ,around G. Obviously, the private niae'net will, therefore, attract its armature and retain the side switch H locked in second position, maintaining; the side switch 37 on the contact point 83. The rot ry niaa'net Q--i being' provided with the interruptor mechanism that comprises the interruptor springs 90 and 91 and the interruptor linger will continue to operate step by step in a Well known manner. soon as the private wiper 30 reaches a nongrr undcfl Contact the energizing circuit t'or the private magnet 1G is broken and the side switch ll is drawn into third position by he retracting; spring; 33. l.Wien the side vh passes to thirr position the subscribefs line conductors 7 1 and are e3;- tcnded through the side switch wipers 97 and 93 to the line wipers 31 and and thence to the trunk conductors 99 and 100 'that lead to the connector F, as shown in Figi', 1. The private wiper 30 connects at the saine time with the trunk release conductor 101. lt is assumed, ot course, for the purpose. et illustration. that all oi" the tiret nine trunks are busv llilhen the side s.vitch wiper passes to third position it engages the cfrouvided contact point 118 and as a result cfiatablishes a eii:,ii; liiig` potential at the conn rotor private banks from the ground terminal G8 by way of the private normal conductor 22. The connection is made from the ground terminal G8 to the Contact point 113, side switch wiper 93 to the private normal relay spring 21, thence to the spring 20 and to the private normal conductor 22. 1t will be seen that when the rotary line -relay 12 presses the springs 17 and 18 together not only is an energizing circuit established through the private magnet 16, but also through the winding 15 of the private normal relay 5. rihe current through this Vwinding` passes Jfrom ground G2 through the springs 13 and 17 and conductor S1 to the winding 15 ot the private normal. relay 5, thence through the battery lead 73 and through battery B to ground Each time that the said relay is energized a guarding potential from the ground GS to the connector private bank is interrupted, but this is oit no importance. Having obtained connection with the connector-switch F the subscriber presses the button 111 twice and airain grounds the vertical line conductor 71 twice. As a' result the vertical line relay 51 of the connector is energized twice by a flow of current from the substation ground terminal G1 to the vertical line conductor 71, thence through the side switch wiper 97 to the contact point 102, conductor 103, line wiper ,31, trunk conductor 99, vertical line relav 51 to the battery lead 73 and through battery B to ,around G. Ot course the vertical line relay or" the first-selector A is also energized over the same circuits that h are been described heretofore; but the energisation ot this relay 10 has no signifi cance at this time. The vertical line relay 51 upon attracting' its armature twice presses the springs 104: and 105 into contact twice, and as a result the vertical magnet 53 is magnetized each time. The current through the vertical magnet passes from ground (i4 throun'h the springs 105 and 104i-, conductor 10F, private springs 107 and 103, conductor 109, side switch wiper 110. contact point 111, vertical magnet 53 t0 the batterv lead 73, then throuph battery B to ground G. T he vertical magnet 53 unon operatinoj twice raises the switch shatt 53 two steps and places the private and line wipers 59, (i0 and 01 opposite the iirst contact of the second level ot the private and line banks 62 and G3, respectively. After pressing` the vertical button the subscriber presses the rotary button 42 once, grounding; the rotary line conductor 13. As a result the rotary line relay 52 of the connector is energized by a flow ci3 current from the substation 4.around G1 to the rotary line conductor 13, thence through the switch shaft springs 14 and 11 of the first-selector and through the bridge-cut-oii relav springs 6 and 7 to the side switch wiper 93, contact point 112, conductor 113, rotary wiper 32, trunk conductor 1.00, rotary line relay 52 to the battery lead 73 and through battery B to ground G. At the same time that the rotary line relay 52 is energized the rotary line relay 12 and the private normal relay 5 ot' the tirst-selector are energized also through the following circuit: From the substation ground G1 to the line conductor 13, thence through the switch shattsprings 14 and 11 to the bridge-cut-oiI relay springs 6 and 7, thence through the conductor 30 to the rotary line relay 12, and to the battery lead 73, then through battery B to ground G. The said rotary line relay 12 upon attracting its armature resses the springs 17 and 18 into contact t iereby sending a flow of current through the winding 15 of the private normal relay 5, as previously explained. Each time that the private normal relay 5 is energized the guarding potential established at the connector private banks by way of the private normal conductor is cut ott for an instant, but this is of no consequence yet.. lVhen the rotary line relay 52 attracts its armature the springs 114 and 115 are pressed together and also the springs 116 and 105. The connection of the former two (114 and 115) is of no consequence at this step, but the engagement of the springs 105 and 116 causes the private magnet 56 to become energized once. As a result the side switch I is tripped into second position. When the side swit h is tripped into second position the side switch Wiper 110 engages the contact point 117, so that the rotary magnet 54 instead ot the vertical magnet 53 is placed under the control of the rotary line relay 51. For the last operation the subscriber presses the vertical button 41 ten times, grounding the vertical line conductor ten times and energizing (over circuits that have already been traced) the vertical line relay of the connector ten times. Each time that the vertical line relay presses the springs 104 and 105 into contat, since the side switch wiper 110 is now shifted as described, the rotary magnet 5t is operated. The current for magnetizing the said rotary magnet passes from ground G* to the side switch wiper 110, as previously described, thence to the contact point 117, and through the rotary magnet 54 to the battery lead 73, then through battery B to ground G. The wipers 59, 60 and 61 having been previously raisedto the second level are now rotated one step at a time and thus carried onto the tenth set of contacts and placed in connection with the normal conductors 22, 119 and 120, respectively, as shown in Fig. 1. It will be remembered that at the first-selector A the private normal conductor 22 is connected to ground GS after the side switch passes to third pesition; therefore. the tenth contact 121 of the second level of the private bank 62 as well as all other connector private bank contacts in multiple therewith are grounded. Ordinarily upon grounding the rotary line conductor 13, after the private wiper 59 has been carried onto a grounded contact, the connector-switch is released. For example, when one subscribers line calls another subscribers line that is busy; but special provision is made in this case, so that a line may call back upon itself even after the first-selector has established a guarding potential, as described. This is accomplished by means of the private normal relay 5 that breaks the connection between the first-selector ground G8 and the private normal bank conductor 22 each time that the rotary line conductor 13 is grounded. When the subscriber presses the rotarv button 42 for his last operation, by grounding the rotarv line conductor 13 he energizes the first-selector rotary line relay 12 and, as a result, the private normal relay 5, as described. At the same time, and in multiple with the said rotary line relay 12, the rotary line relay 52 of the connector is energized over circuits that are known, and as a result the private magnet 56 is also energized. The private manne-t 56 upon attracting its armature permits the escapement finger 122 to clear the tooth 123, and the side switch retracting spring 124 then draws the side switch I to third position bet'ore the private magnet denergizes and before the private normal relay 5 denergizes and restores the ground connection to the private contact point 121. It a guarding potential were not removed from the contat point 121, as in the case where one subscriber calls another subscriber whose line is busy, the release magnet 55 would be energized by a flow of current from the grounded terminal of the battery B to the private contact point with which the private wiper 59 is in contact` thence through the side switch wiper 125. contact point 126. conductor 127. line relay springs 114 and 115, conductor 128. release magnet 55 to the bat# tery lead 73 and through battery B to ground G. The release magnet 55 then attracts its armature, releasing the shaft 58 and side switch I in the usual and wellknown manner. As soon as the side switch passes to third position the side switch wiper 125 engages the contact point 129 and the private wiper 59 is placed in connection with the ground terminal G5. As a result the private normal conductor 22 is connected to ground from the opposite direction. and since the private normal relav springs 19 and 20 are now in contact the said relav 5 and the bridqe-cut-o' relav 2 are locked bv the energizing current that flows from the said private normal conductor 22 through the said springs 20 and 19 to the winding 4 of the private normal relay 5. thence through the bridge-cutol relay 2 to the battery lead 73 and through battery B to ground G. As a result of energizing the bridge-cut-olf relay 2 the vertical line relay 19 of the selector A disconnected from battery B and the rotary line relay 12 is disconnected from the rotarv line 13, so that when ringing current is projected back on the line there will be no danger of these relays being energized and causing some interference with the connection. It is also desirable, of course, to have the line as free of bridges as possible during talking. After establishing the connection the subscriber at the substation C presses the signaling button 139, causing the spring 131 to leave the contact point 132 and to engage the grounded contact point 133. As a result the vertical line conductor 71 is grounded over the following circuit: from ground G1 to the conductor 134, springs 135 and 136, ground springs G5 and 64, Contact point 133, spring 131, secondary springs 69 and 70, contact point 45, spring 43 to the vertical line conductor 71 and, of course, the vertical line relay 51 of the connector becomes energized. Since the side switch wiper 110 is now in third position in engagement with the contact point 137, when the vertical line relay 51 becomes energized the ringer relay 57 responds. Magnetizing current `passes from ground G4' to the side switch wiper 110, thence to the contact point 137 and through the relay 57 to battery lead 73, thence through battery B to ground Gr. lVhcn the ringer relay becomes energized the springs 138 and 139 are pressed onto the ringer generator springs 140 and 141, respectively, so that a ringing current 1s sent back to the calling line over the following circuit: from the ringer generator 142 through the ringer relay springs 141 and 13 9 to the side switch wiper 143, contact point 144, wiper 60, normal conductor 119 to the vertical line conductor 71, thence through the ringers of various stations, whose receivers are on their hooks, hack to the rotary line conductor 13, thence over the rotary normal conductor 120, rotary line wiper 61, Contact` point 145, side switch wiper 146. ringer relay springs 138 and 149 to the ringer generator 142. The ringing current furnished by the ringer generator 142 is adapted to ring only the bell at the substation :#1225 and so that subscriber responds. 1t inay be sta-ted that the connector switches are divided into groups and each group is connected with a ringer generator which provides a ringing current of a different frequency, so that when a subscriber of a certain group is called the calling subscriber automatically selects a connector switch which is equipped with suitable ring-inpcurrent for operating the ringer of the desired line only. The other ringers, however., which may be bridged across the line are not operated,

since they are so tuned or adjusted as to respond to ringing current of a different character. When he' removes his receiver his talking set is bridged across the vertical and rotary line conductors, just as the talking set of the substation-C and, of course, the two subscribers can then converse. After the conversation has terminated the calling subscriber may hang up his receiver and press the release springs 48, 49 and 50 of his telephone together and thus ground the verconductor 71 to the vertical normal conductor 119 (Fig. l), thence to the vertical line wiper (more clearly shown in Fig. 3) to the contact point 144, side switch wiper 143, ringer relay springs 139 and 149 to thev vertical back-bridge relay 147, thence to battery lead 73 and through battery B to ground The current for the rotary back-bridge relay 148 flows from the rotary line conductor 13 to the rotary normal conductor 120 (Fig. 1) thence to the rotary line wiper 81 (Fig. 3) to the contact point 145, side switch wiper 146, ringer relay springs 138 and 150, through the rotary back-bridge relay 148 to the battery lead 73, and through battery B to ground G. Said relays upon attracting their armatures simultaneously press the springs 151, 152 and 153 into contact. The engagement of the springs 152 and 153 enorgizes the private magnet 56, the magnetizing` current flowing from ground G6 through the springs 153 and 152, conductor 154 to the private magnet 56, thence through said magnet to the battery lead 73 and through` battery B to ground G. The private Inag net upon becoming energized attracts its armature and separates the springs 108 and 107, whereby the energizing circuit through the ringer relay 57 is broken; bearing in mind that the vertical line relay 51 is also energized at this time, which operates to close an energizing circuit through the rin ger relay 57. as previously explained. The said spring 151 being now in engagement with the springs 152 and 153 a circuit is established through the release magnet 55 over which current Hows for energizing the said release magnet 55. The circuit extends from ground G6 through the springs 153, 152 and 151 to the conductor 156, release magnet 55 to the battery lead 73, thence through battery B to ground Gr. The release magnet 55 upon becoming energized attracts its armature 157, which latter then restores the double dog 158, and as a result the switch-shaft 58 and the side switch I are restored to normal position. As soon as the side switch Wipers 143 and 146 leave the contact points 144 and 145 the energizing circuit for the back release relays 147 and 148 is destroyed, so that the said relays 147 and 148 regain their normal condition, permitting the private magnet 56 and the release magnet 55 to regain their normal condition also. It Will also be understood that as soon as the side switch wiper 125 leaves the contact point 129 of the connector the circuit that has up to that time retained the private normal relay 5 of the first-selector energized (which circuit includes the Winding 4 of the relay 5 and the bridge-cutoff relay 2) is destroyed. As soon as the bridge-cut-oi relay springs 6 and 7, and 8 and 9 ree'ngage, the vertical and rotary line relays l0 and 12 of the selector A will in turn become energized simultaneously. As a result of the energization of the rotary line relay 12 the springs 17 and 18 are brought into contact and the private magnet 16 is also energized over circuits that have been described. Upon becoming energized the said private magnet separates the private springs 76 and 77 and presses the spring 77 into engagement with the spring 159. The engagement of these last tWo springs 77 and 159 places the release magnet 25 in connection with the vertical line relay spring 74, so that as soon as the said spring 7 4 engages the spring 18 the release magnet 25 becomes energized by a flow of current from the ground termlnal G2 through the private springs 77 and 159 and through the release magnet 25 to the battery lead 73 thence through battery B to ground G. The release magnet 25 then attracts its armature 160, whereby the release link 161 latches the double dog 27, and when the release springs 48, 49 and 50 at the releasing substation disengage, the vertical and rotary line relays 10 and 12 deenergize, denergizing in turn the release magnet 25 and permitting the retracting spring 162 of the release armature 160 to restore the double dog 27 to normal condition, and as a result the switch-shaft 26 and side switch H are also restored in a Well known manner to normal condition. If a subscriber at the substation #320 attempts to use his phone while the subscribers C and D are using the line, the substation relay 163 becomes energized when the receiver 164 permits the switch-hook 165 to rise, and as a result the substation ground G7 is cut off from the control of the substation E when the springs 169 and 170 are separated.

The energizing current for the said relay 163 flows from ground Gr7 through the springs 166 and 167, relay 163, springs 168 and 169 to the rotary line conductor 13, thence it passes to the rotary normal conductor 120 (Fig. l), rotary line Wiper 61 et the connector (Fig. 3), contact point 145, side switch wiper 146, ringer relay springs 138 and 150, rotary back-bridge relay 148 to the battery lead 73 and through battery B to ground G. Before the connector F has made connection With the line the energizing circuit instead of extending over the rotary normal conductor 120, as described, passes through the switch shaft springs 14 and 11 of the first-selector and through the bridge-cut-of relay springs 6 and 7 to the rotary line relay 12, thence through the said relay to the battery lead 73 and through battery B to ground G. It will be seen that when the called subscriber raises his receiver, on answering, he will also be locked out, as shown, over circuits similar to those described in connection with station #320. By the term locked out is meant that the locking relay 40 which tontrols the ground connection at the subscribers substation becomes energized and operated to cut off the ground, thus rendering the telephone useless so far as the operation of the central office switching apparatus is concerned. When the substation relay operates to break the substation ground connection, it may be restored when the subscriber restores his switch-hook. As a result the link 40 depresses the substation relay armature, which latter then permits the controlled springs to be restored. It Will be noticed that during the releascgthat is, when both the vertical and rotary line conductors are grounded simultaneously-a circuit is established through the vertical line relay 51 of the connector at the same time the circuit is established through the backbridge relay 147, which circuit through the vertical line relay 51 is already known. It might be expected that since the side switch wiper 110 is in third position the energizing of the said vertical line relay 51 might cause the energization of the ringer relay 57 in turn, which latter would then break the energizing circuit tor the back-bridge relays 147 and 148 by separating the ringer .relay springs 138 and 139 from the ringer relay springs 15() and 149, but the relays and springs are so adjusted that the back-bridge relays 147 and 148 respond much quicker than the vertical line relay 51 and much quicker than the ringer relay 57. Therefore, the release occurs betere the ringer relay 57 has time to energize. It WillA be clear from what has preceded that a connection may be made to another line by operating the switches in the saine manner that has been described in the preceding, the only difference being that instead of the normal conductors 119 and 1&20 leading back to the calling line they lead to some other subscribers line, and in that event if the desired line is busy the encrgization of the private normal 5, each time that the rotary line conductor 13 is grounded, will not remove the guarding potential from the called subscribers private bank contact- Therefore, if the called line should be bu the connectorsswitch 1T will he released, as already described. 1t the connection is established the calling subscriber will ring the desired line in the same manner that he rings his own line. lt will be uiulerstood that when the connector side switch passes to third position and the private wiper 59 is grounded, the private normail conductor that leads to the bridge-cut oii relay of the called first-selector will also be grounded7 and the said bridge-c'ut-ot rela;r will be energized, thus removing the vertical and rotary line relays of the called first-selector from across the line. This relay Q will be restored as soon asthe connector-switch is restored, since when the said connector-shalt falls the ground connection is again removed Yfrom the private normal. It the called line should be another party line a third subscriber who attempts to use the line from the side oi' the called line will be locked out, because his substation relay that controls the substation ground will become magnetized over the rotary normal conductor in the same manner that the substation relay 163 was shown to energize over the rotary normal conductor 120 (Fig. 1). On the other hand, ii a third subscriber tries to interfere on the calling line (the substation E, for example), the relay 163 will be energized not over the rotary normal 120 but by a new path which, after leaving the rotary line conductor 13, extends through the switch shaft springs 14 and 11, backbridge relay springs G and 7, through the rotary line relay 12 to the battery lead 78 and through battery B to ground G. This path is available since the bridge-cut-oirelay 2 is not energized because the line allotted to the selector A is not being 'called and, therefore, lthe bridge-cutoff relay springs 6 and 7 are in contact as well as the switch shaft springs 14 and 11. The release, when two diiiercnt lines are connected, may be initiate d by the calling subscribed. When the calling subscriber releases he grounds his line conductors 71 and 18 and energizes the vertical and rotary line relays oi the iirstselector and the vertical and rotary line relays et the connector simultaneously over the circuits that are known and which have been described. in a manner previously explained, and the connector will be released as follows: The line relay 52 upon energizing presses the springs 114 and 115 into contact and also the rlfhe first-selector will be released springs 116 and 105 into contact. The latter two, as is well known, energizes the private magnet 56, which latter magnet then closes connection between the private springs 107 and 155. The closure of the springs 114 and 115 iinally connects the release magnet 55 (since the private springs 107 anc 155 are in contact) with the vert-ical line relay spring 104. The vert-ical line relay 51 being energized presses the spring 104 onto the spring 105, thus .mag` etizing the release magnet 55 by a flow ot current from ground Gt through the line relay springs 105 and 104, through the private springs 107 and 155, and through the rotary line relay springs 114 and 115 to the release magnet 55, and through the said magnet to the ba tery B. As a result the connector side switch and sha-ft will be restored, and when the release springs at the releasing substation separate, all the relays and magnets of the circuit that have been in use will regain normal condition.

In the first-selector the bridge-cut-oil relay may be of any suitable resistance, but

results are obtained with a coil of thirteen hundred ohms. Then private normal relay 5 gives satisfaction` when the winding 4 is made of a resistance 01"' five hundred ohms, and the winding 15 oit' two hundred and fifty ohms.

VJ hen one lino is connected with another it is evident that the voice-currents pass through the condensers.

From the foregoing it will be seen that 1 provide improved means for 'enabling a party line subscriber to call back on his own line, so to speak, and for preventing the connector from being automatically re-4 leased, theguarding potential being removed at the time that the connector seizes the normals leading from the line to the connector bank contacts.

lt will be seen that the two line relays 10 and 1Q of the first-selector are bridged across the subscribers telephone line, but that the rotary relay has its end of the bridge normally disconnected from the said line, this normally open connection being closed by the contacts 11 and 14 out the normal post switch as soon as the selector is given the iirst vertical step. As previously explained, the, private normal controlling` relay 5 is double wound, and has one winding adapted to be energized in series with the bridge-cuto@ relay 2, and has its other winding adapted to be energized over a separate circuit controlled by its own contacts.

di hat 1 claim as my invention is z- 1. In a telephoneexchange system, a telephone line, a pair of relays bridged across the said line, a private normal for( said line, a bridge-cut-oii relay, a private normal relay controlling the continuity of ksaid private normal, and a circuit for energizing the lastmentioned two relays in series,

2. An automatic telephone exchange system comprising a selector, trunk lines to' be selected by said selector, means for causing said selector to perform a trunking operation in accordance with a digit of the called number, said selector provided with a bridge, a bridge-cut-oif relay, a private normal, a private normal controlling relay, and a circuit for energizing said relays in series.

3. An automatic telephone exchange system comprising a subscribers telephone line, an automatic switch individual to said line, said switch provided with a bridge, a bridgecut-off relay, a private normal, a private normal controlling relay, and a circuit for energizing said relays in series.

4. An automatic telephone exchange system comprising a selector, trunk lines to be selected by said selector, means for causing said selector to perform a trunking operation in accordance With a digit of the called number, said selector provided with a bridge, a bridge-cut-of relay, a private normal, a private normal controlling relay, and a circuit for energizing said relays in series, said private normal relay provided with an additional energizing circuit, and said bridge including a relay controlling said additional energizing circuit.

5. An automatic telephone exchange system comprising a subscribers telephone line, an automatic switch individual to said line, said switch provided with a bridge, a bridgecut-off relay, a private normal, a private normal controllin relay, and a circuit for energizing said re ays in series, said )rivate normal rela provided with an ad itional energizing circuit, and said bridge including a relay controlling said additional energizing circuit.

6.' An automatic telephone exchange system comprising a subscribers telephone line, a private normal for said line, and an individual switch for said line, said individual switch provided with a private normal controlling relay having two windings, and parallel energizing circuits each including one of said windings, one of said energizing circuits controlled by the relay itself.

7. In a telephone exchange system, the combination of a telephone line, a pair of relays bridged across the said line, a private normal for said line, a bridge-cut-ofil relay, a private normal relay controlling the continuity of said private normal, a circuit for energizing the tivo relays in series, a bell or electric ringer at each substation, a source of ringing current at the exchange or central station, a ringer relay for bridging the source of ringing current across the line of any called substation, and a circuit for energizing said ringer relay after connection is established with the line of the called substation.

8. In an automatic telephone exchange system, the combination of a selector, trunk lines to be selected by said selector, means for causing said selector to perform a trunking operation in accordance with a digit of the called number, said selector provided with a bridge, a bridge-cutoff relay, a private normal, a private normal controlling relay, and a circuit for energizing said relays in series, a bell or electric ringer at each substation, a source of ringing current at the exchange or central station, a ringer relay for bridging the source of ringing current across the line of any called substation, and a circuit for energizing said ringer relay aftcrvconnection is established with the line of the called substation.

9. In an automatic telephone exchange system, the combination of a subscribers telephone line, an automatic switch indi vidual to said line, said switch provided With a bridge, a bridge-cut-off relay, a private normal, a private normal controlling` relay, and a circuit for energizing said rclays in series, a bell or electric ringer at each substation. a source of ringing current at the exchange or central station, a ringer relay for bridging the source of ringing current across the line of any called substation, and a circuit for energizing said ringer relay after connection is established with the line of the called substation.

10. In an automatic telephone exchange system, the combination of a selector, trunk lines to be selected by said selector. means for causinnr said selector to perform a trunl'- ing operation in accordance with a digit of the called number, said selector provided With a bridge, a bridge-cut-off relay, a private normal, a private normal controlling relay, and a circuit for energizing said relays in series, said private normal relay provided With an additional energizing circuit, and said bridge including a relay controlling said additional energizing circuit, a bell or electric ringer at each substation, a source of ringing current at the exchange or central station, a ringer relay for bridging the` source of ringing current across the line of any called substation, and a circuit for encrgizing said ringer relay after connection is established with the line of the called substation.

11. In an automatic telephone exchange system, the combination of a subscribers telephone line, an automatic switch individual to said line, said switch provided with a bridge, a bridge-cut-off relay, a privatel normal, a private normal controlling relay, and a circuit for energizing said relays in series, said private normal relay provided With an additional energizing circuit, and said bridge including a relay controlling said additional energizing circuit, a bell or electric ringer at each substation, a source of ringing current at the exchange or cenllt) telephone line, a private normal for said linet andan individual switch :fer said line,

said individual switch provided with a private iniiiuali trolling relay having tivo windings.` and parallel energizing circuits each .including one el said Winnings, one oli said energizing` circuits ccntrolled by the relay itself, a bell or electric ringer at each substation, a source ol" ringing current at the exchange or central station, a ringer relay for bridgingtlie source oiI ringing current acres-s the line of any called substation, and a circuit for energizing said ringerl relay after connection is established with the line ofthe called substation.

13. In a telephone exchange system, the combination of a telephone line, a pair of relays bridged across the said line, a private normal for said line, a bridge-cut-oil relay, a private normal relay controlling the eontinuity oi said private normal, a circuit for energizing the tivo relays in series, and a ground connection at each substation, said ground connections normally disconnected from the telephone line conductors, but each ground connection adapted for use by its allotted subscriber inperforming a separate ground impulse transmitting operation for each digit of any called number. i

14. 1n an automatic telephone exchange system, the combination ot' a selector, trunk lines to be selected by said selector, `means for causing said selector to perform atrunking operation in accordancewitli a digit of the called number, said selector provided with a bridge, a bridge-cut-oli relay, a private normal, a private normal controlling relay, and a circuit for energizing said re.

lays in series, and a ground connection at each substation, said ground connections normally disconnected from the telephone line conductors, but each ground connection adapted for use by its allotted subscriber in performing a separate ground impulse transmitting operation for each digit oiE any called number.

15. In an automatic telephone exchange system, the combination of a subscribers telephone line,an automatic switch individual te said line, said switch provided with bridge, a bridge-cut-oii relay, a private normal, a private normal controlling` relay, and a circuit for energizing said relays in series, and a ground connection at each substation, said ground connections normally disconnected from the telephone line conductors, but eacli ground connection adapted for use by its allotted subscriber in performing a separate ground impulse transinitting 4operation i'or each digit of any called number. y i .f

16. In an automatic telephone exchange system, the." combination of a selector, trunk lines toy be selected by said selector,

"means for causing said selector to perform` trunlring operation in accordance with a digit of the called number, said selector provided With a bridge, a bridge-cut-oi relay, a private normal, a private normal controllingrelay, vand a circuitfor energizing said relays in` series, said' private normal relay providedwith an additional energizing circuit, and said bridge including a relay. `controlling said additional energizing l circuit, and a ground connection at each substation, said ground connections normally disconnected from the telephone liney conductors, but eacli ground `connection adapted for use by its allotted subscriber in performing a separate ground transmitting operation for each digit of any called number.

impulse i 17. 1n an automatic telephone exchange leach digit of any called number.

18.111 an automatic telephone exchange system, the combination of a subscribers telephone line, a private normal for said line, and an individual switch for said line, said individual switch provided With a private -normal controlling` relay having tivo windings, and parallel energizing circuits each including one of said windings, one of said energizing circuits controlled by the relay itself, and a ground connection at each substation, said ground connections normally disconnected from the telephone line conductors, but 4each ground connection adapted Yfor use by its allotted subscriber in performing `a separate ground impulse transmitting operation Jfor each digit oi' any called number.

19. ln a telephone exchange system, a telephone line, a pair iol relays bridged across the said line, a private normal for i said private normal, acircuit for energizing the lastmentioned two relays in series, `and means having non-rotary motion to select` groups and then rotary motion to confnectwith the Icalled line in; any group selected by the non-rotary motion' of the same means, both motions controlled over said "t'eleplorieilifi from the substation thereof. 2O. An automatic telephone exchange' system comprising a selector, trunk lines to be selected by said selector, means or causing said lselector to perform a trunkmg operation iii-accordance with a digit of the called number,`said selectoriprovided with 'alridge across the conductors of 'the talk- -ing circuit, a relay in said"bridge for con- 1. trolling sadselector, a bridge-cut-oi relay, fafprivatenormalfa'private normal controlling relay, and-a circuit for energizing said relays'in series, said selector having one motlon to 'select groups, and then rotary intion to find a line in any selected group 'controlled by 'elements in said bridge.

' 21. An automatic telephone exchange system comprising a subscribers telephone hnega'n automatic switch individual to said line, said switch provided with a bridge 'across the conductors of the talking circuit,

a 'relay in said bridge for controlling said means? switch, a bridge-cut-o relay, a private normal, a private normal controlling relay, and a circuit forvenergizing said relays in series, said selector having one motion to select groups, and then rotary motion to find a line in any selected group controlled by elements in said bridge.

" 2. An automatic telephone exchange system comprising a subscriberfs telephone -line, a private normal for 'said line, an individual switch fory said line, said individual switch provided with a private normal controlling relay havingtwo windings, parallel energizing circuits each including one of said windings, one of said energizing cir-v cuits controlled by the relay itself, and

WILSON L. CAMPBELL.

Witnesses:

EDWARD D. FALES, ARTHUR B. Srmr. 

